Monthly Archives: January 2013

Semiconductor Assembly and Test Services are converting rapidly into a pure outsourcing mode of operation. While today perhaps only 50% of the market is using Outsourced Semiconductor Assembly and Test (OSAT, or SATS) this number is set to increase in the future.

While many of the low-end suppliers are competing on price-driven products the top 4 leaders (ASE, AMKOR, STATS and SPIL) are chasing the big expensive packages that requires large investment and new technologies. In fact, packaging has become gradually as complex and as costly as silicon technology. As the industry is moving to 3D packaging solutions there will be numerous cases where the package cost will be higher than the silicon cost.

ASE, AMKOR, STATS ChipPAC and SPIL are competing on packaging, assembly and test markets for the last 10 years. These 4 leaders are constantly developing new technologies and business models to generate economic profit.

In the future a massive investment will be required in order to support new trends and technologies, therefore, many analysts believe a market consolidation will be required. Investment in copper wire, 3D packaging and TVS, just to name a few, requires very deep pockets.

Semiconductor Assembly and Test Leaders

Let’s look at the top four assembly companies: ASE, Amkor, SPIL and STATS ChipPAC in more detail.

The top companies and their respective sales positions are shown in the graph; it covers their financial growth from 2002 to 2011. ASE continues to remain in the top spot, with AMKOR, STATS ChipPAC and Siliconware Precision Industries Ltd. (SPIL) in second, third and fourth places respectively.

We believe that the SATS industry will see a growth in the following years due to the shift into outsourcing model and due to the increase in complex package cost.

QFN package is probably the most successful package type today. Offering low price, excellent performance and small size, it is an ideal package for many applications.

QFN (quad-flat no-leads) is a plastic SMT package consisting of: a leadframe, single or multiple dies, wirebonds and a molding compound. The leadframe is the heart of the package and therefore the size and the dimensions of the leadframe determine the overall package performance.

QFN package production process

The following diagram shows the necessary steps in the assembly process of QFN package.

Pins and Pads/leads

All QFN’s are leadless packages where electrical connections are made via pads on the bottom

surface of the package. These pads are soldered directly to the PCB.

The standard QFN has a paddle (exposed pad) which enhances the thermal and electrical characteristics enabling heat transfer and RF applications.

Downbonds

Downbonds are wirebonds which are connected directly to the exposed pad, typically for better ground connectivity.

Punched QFN vs. Sawn QFN

Punched and sawn QFN are slightly different, the illustration below shows the difference in the molding compound shape. The shape is a result of the different simulation process, and normally does not introduce any issues in the performance or in the target PCB soldering process.

QFN Thermal Performance

In addition to the excellent electrical performance QFN provides superb thermal performance through the paddle (exposed pad), which allows a direct thermal conductivity for removing heat from the die.

It’s important to note that QFN package is relatively small thus the capabilities of dissipating heat without air flow are somewhat limited.

Other names for QFN

Thanks to the benefits of QFN package and the successful market penetration, most of the assembly houses provide QFN packaging services; however, they are using different names.

There are many ways to deliver, package and transport silicon products. Here’s a short primer that provides the basic facts regarding how silicon can be packed and delivered to ensure safe transportation with minimum damages.

There are two main options for receiving wafers from your foundry: tested or untested.

Untested wafers. This would be the “plain vanilla” delivery format. Wafers are delivered from the fab without being tested electronically. The wafers only go through visual inspection in order to detect visual defects, but are not functionally tested by any ATE.

Tested wafers.In this case, the wafers have been already tested and associated with a wafer map (file) indicating the pass and failed silicon dies. In this case, the tested wafers go through an electronic testing process (ATE), which is usually called Wafer Sort and conducted by a test house or the fab itself.

Some test houses still offer die inking instead of electronic wafer maps, but this method is not recommended today for wafer delivery. Inking is just more expensive than an electronic file.

Wafer delivery options

Wafers Cassettes

Wafers (tested or untested) are delivered in wafer cassettes – plastic housing providing protection during transportation and storage. Cassettes can be stacked and are ideal for further post processing. Cassettes can be easily inserted into a various machines (for instance: wafer testing) for automatic handling. An ATE can access all the wafers in a cassette without any human intervention.

Wafers Carrier Boxes

For more robust packaging, wafers can be stored and shipped in carries (pizza) boxes. This method is not ideal for automated post processing because each box has to be manually opened and closed after processing. Wafer boxes have a smaller size than cassettes.

Die Delivery Formats

Silicon dies are separated from the wafer via a dicing or sawing process. Typically, wafers coming out of the foundry are approximately 750um thick to ensure maximum robustness during shipping. Before dicing wafers typically go through a back grinding (or backgrinding) process to thin down wafers to 75um to 50um. This step is mandatory in order to get the die into small packaging. The dicing process is performed by a mechanical sawing that saw in X and Y directions or by a laser cutter if more flexibility is required.

Known Good Die (KGD)

These are silicon dies which have been electronically tested before being placed in the carrier. A typical KGD is a result of a tested wafer that has been diced.

A KGD is the recommended method of delivery when the final product is a component consisting of multiple silicon dies. In this case, the known good dies are delivered to the assembly house from one or more foundries.

Dies on a waffle pack

Silicon dies can be delivered in a tray which is also known as waffle pack – a plastic tray with pockets that match the die size. A waffle pack has a lid and is delivered in an antistatic bag. Waffle packs are ideal for delivering small number of silicon dies, typically from a MPW process.

Dies on Blue Tape

Before wafer dicing, an adhesive tape is applied to the wafer together with a metal frame. After dicing the dies are glued to the membrane ready to be entered into the pick and place machine for assembly. The two most popular adhesive tapes are blue film and UV film. Blue film is approximately 1/3 of the cost of UV film

Dies on Gel Pack

Gel Pack provides more protection than a waffle pack and yet they can be easily removed. The carrier prevents die damage that can occur from contact with the edges or top surface of the carrier. Using surface tension, dies are held in place and protected, even if the carrier is tilted, or turned upside down.

Components Delivery Format

Components are packaged silicon dies.

Blind Assembly

Blind assembly is a term that describes untested silicon dies (in wafer format) that are about to be assembled into a package. In cases when the yield is high so that wafer testing is more expensive than the packaging cost of bad devices, the wafer testing step can be skipped.

Tested Components

These are components which are tested after the assembly process. After this step the components qualify to be assembled on the PCB.

Components in Tray

Larger components such as BGA packages are shipped in a matrix tray that complies to the JEDEC standards. Typically, JEDEC trays have the same ‘x’ and ‘y’ outer dimensions and are easily stacked for storage and manufacturing. Components are also arranged in the trays to match industry standards.

Components in Tape and Reel

As indicated by its name, this is a method of covering parts in separate pockets in a long continuous plastic strip. The reel is a very common method for ‘feeding’ small components to automated PCB assembly equipment.

Components in Tube (stick)

Sticks (or tubes) are constructed of rigid clear or translucent polyvinylchloride (PVC) material. The sticks have standard outlines that meet current industry standards, and protect components during shipping and handling. Sticks fit perfectly to feeder systems for automated assembly or testing.

Dry Packing of Components

This method involves a baking process for plastic packages such as BGA and QFN, to remove the moisture from these vulnerable devices and avoid a popcorn effect. The baking time is driven from the number of days or hours the components should be exposed (outside the pack) before being assembled on a PCB.